In sawmills, logs are cut into slab sided articles of wood in the process of converting the logs into useable lumber. For this purpose, the log is fed into a device referred to as a chipper or canter (hereinafter “chipper/canter”). The chipper/canter has a rotating cutting head incorporating a plurality of cutting members, typically removable knives, saws, or combinations thereof. The cutting head is variously referred to as a chipper head, canter head, slabbing head, or conical head. The term “chipper” refers to one function of the chipper/canter, i.e., to produce chips that are used to form other wood products, such as oriented strand board. The term “canter” refers to another function of the chipper/canter, i.e., to cut a piece from the log, referred to as a “cant,” having at least two parallel, substantially flat or slab sides, and the term “slabbing” refers to producing one or more of these sides. All of these heads are termed “conical” heads due to their geometry; the cutting surface defined by rotation of the head is actually frustoconical in shape.
The cutting head rotates about its axis of symmetry and the log is translated toward the head in a direction that is aligned with the longitudinal axis of the log and perpendicular to the axis of rotation of the head, causing the log to interfere with the cutting surface of the head and thereby cutting the log to produce both elongate, slab sided articles of wood and chips.
There are typically two opposed cutting heads operating on the log at substantially the same time to produce, during one pass of the log, two sided cants, and often there are four cutting heads for producing four sided cants from the log in a single cutting operation.
As the cutting surface defined by the rotating conical cutting head is actually frustoconical, it includes a flat annular portion as well as a conical portion that flares outwardly from the annular portion. The plane of the annular portion of this cutting surface is in the plane of the slab sides of the articles of wood and produces a finish on these sides. However, the log first encounters the conical portion of the cutting surface of the rotating cutting head, which cuts and tears chips from the log in preparation for the finishing provided by the annular portion as translation of the log in the direction just indicated is continued.
It will be appreciated that a significant quantity of the log must be removed as chips because the cross-section of the log is roughly circular while it is desired to cut pieces from the log whose cross-sections are rectilinear (hereinafter “lumber”). However, even though the chips themselves have economic value, it is often desirable to minimize the degree to which the log must be reduced to chips in favor of producing lumber.
The aforedescribed annular portion of the cutting surface defined by the rotating conical cutting head is typically produced either by a plurality of circumferentially spaced knives, or a disk-saw. Any such structure is referred to hereinafter as a “facing” portion of the cutting head because it produces a “facing” cut on the log that defines the slab sides of the lumber.
The aforedescribed conical portion of the cutting surface is typically produced by a plurality of staggered knives that are often arranged in spaced apart circular patterns, or alternatively in a spiral pattern, so as to trace a frustoconical surface as the head rotates. Any such structure is referred to hereinafter as a “chipping” portion of the cutting head because it cuts chips from portions of the log that are not used to produce lumber. The knives of the chipping portion are attached to a body of the head either directly or through intermediate members, and the body of the head may or may not itself be frustoconical in shape, a configuration which is often referred to in the art as “solid.”
The surface finished produced by the cutting head is affected by a number of factors, e.g., the extent to which the cutting head is in balance, the density of cutting elements, the speed of rotation, the speed of travel of the lumber, and the ability of the apparatus to efficiently keep chips away from the cutting surface as it is being cut. It has been observed in the course of practice that the best surface finishes are typically provided by cutting heads employing facing portions incorporating disk-saws rather than knives. Still, the surface finish provided by the cutting head, at least in the first instance of processing raw logs, is not as fine as would be desirable. The cut lumber is therefore oversized to allow additional removal of material in subsequent finishing steps, to refine the surface finish. The removal of this additional material, typically in the form of sawdust, represents a waste of material and consumes processing resources. Therefore, it is important to improve the surface finish provided by the cutting head, and there is a need for a conical chipper/canter head providing such an improvement.